Multiple transmitting system



MULTIPLE} TRANSMITTING SYSTEM Filed Jan. 14, 1932 M. LANGER W. RABANUS ATTORNEY IN VE N TORS Patented Jan. 15, 1935 UNITED STATES signers toSiemens and Halske Aktiengeselb schaft, Siemensstadt', near Berlin,Germany, a

company of Germany Application January 14, 1932, Serial mama In GermanyJanuary 20, I931 p Y 11 Claims. (Cl. 179-78) The invention relatesto-amethod of reducingthe cross-talk in multiple lines in which'severallines carry the same signals. Such multiple transmission (news, music,picture signals) may have the advantage that the disturbance or thetransmission on one line, such as an interruption or short circuit ofthe line, does not disturb the transmission on the other lines. Othercases frequently occurring represent the broadcasting systems (wiredwireless) common cable or on the same or adjacent carriers, then as soonas voice currents flow in one or more of these lines hereafter referredto as disturbing lines, noise potentials are induced in the other lineshereafter referred to as the disturbed lines, the occurrence of which isknown as cross-talk. The greater the amplitudes of these voice currentsthe greater will be the crossgo talk disturbance. A certain potentiallevel must therefore not be exceeded in the disturbing lines which carrythe voice currents, so that noise or cross-talk potentials will remainbelow the maximum allowable value or limit in the disturbed lines.However, the level of the crosstalk in the disturbed lines rises only toa small extent if severalv disturbing lines are carrying varioustextssimultaneously instead of one line, since in the individualdisturbing lines the peaks of the disturbing potentials occur atdifferent times. a a

It is a different matter, however, if a plurality of disturbing linesare simultaneously carrying the same text, a case which occursparticularly fregrams (music transmission). Here the disturb ingpotentials occurring simultaneously through the transmission of the samebroadcast performances in adjacent lines, for example of the same noiseor cross-talk potential will not be exceeded in the disturbed lines. Thereduction of amplitude, however, may be of great disadvantage for thetransmission or the performances, since it reduces the ratio of theprogram transmission level to the noise level of the line.

In accordance with the pres'entinvention the reduction 01' theamplitudes is avoided by the fact that the transmission of the sametexts takes place in the individual disturbing lines or groups of lineswith a phase displacement.

. For example, it is possible to displace the dis If a number oftelephone lines are laid in aquently in the transmission of broadcastpro nothing. came a as i ai ntiaitaesfwan lie; spect to each other inphase electrically or by, very slightamountsof time, inwhich theoscil'1a-.

tions arestill quasi-stationary, so thatthe potentials induced in the,disturbed wires by the adjacent disturbing wires for the mostpart arecancelled in their total effect onaccount otthe mutual phasedisplacement. Thesmall; tempo; rary displacement may for example, beoigreat,

advantage for telegraphy (direct current,.-impulse oralternating currentand also infra low frequency telegraphy). Speech ,and music in whichsmall interferences arequasi-stationary,

are also. fieldsptapplication. 3

Another embodiment of theinventive idea may consist in the factthatdisplacements take place in the individual wires in suchspacesoftime that difierent texts, that; iszthe multiple transmissions;

efi'ected, for. example, broadcasttransmissions,

may take place with undiminished-amplitude;

A further advantage of the method inaccordance with the inventionthat-the cross-talk occurring is unintelligible, I which is veryimuch tobe desired from the point of viewoi secrecy. The line level may. alsobev rendered dependent only upon the noise level, so the noise level maybe permitted tobe higher. p

The invention may be-more-iully understood b referringto the drawing ofwhich:

Fig. 1 illustrates oneembodiment of the invention in which the phases ofthe disturbing cur rents in the various lines are reversed.

Fig. 2 illustrates another-embodiment of the in. vention in -whichthe'disturbing, currents are TENT FF-IC transmitted to groups of lineswith a time .dis-.

placement.

Fig. 3 shows still another embodiment of the invention employingelectrical networks to secure different time delaysin .thedisturbingcurrents transmitted to the various linesof the group.

Fig. 1 shows the arrangementin which the energy to be distributed on thecable at l is conveyed to a transformer 2.from whose secondary side twopairsof bus-bars3, 4 are branched off, whose potentials for all thefrequencies are displaced in phase by 180. Now if one or more lines suchas 11 and 13 of cable 16 are connected to the pair ofbus bars 3. (asshown) they will each induce cross-talkin. other adjacent: lines such,as 15 which. will add directly and give risetothe sum of the cross-talkproduced by each of the lines ll or13 alone- Similarly, one or morelines 12 and 14 connected to bus bars 4 will induce crosstalk in thedisturbed circuits 15 which are shown connected to other apparatus 18.This cross-talk will be the sum of that induced by each of the lines 12or 14 alone. .However, since the currents in lines 11 and'13 connectedto bus bars 3 are Just opposite to or 180 out of phase with the currentsin lines 12 and 14 connected to bus bars 4, the cross-talk currentinduced by these two groups of lines 11 and 13, and 12 and 14 in thedisturbed circuits or lines 15 will also be opposite in phase andtherefore will tend toneutralize each other. The resultant cross-talkinduced in adjacent circuits or lines 15 from a plurality of disturbinglines or circuits all simultaneously carrying the same signal is thusreduced without reducing the currents in the individual disturbingcircuits which are all carrying the same signal.

The cross-talk induced in adjacent circuits may be further reduced byuniformly distributing the lines which are simultaneously carrying thesame signal between bus bars 3 and 4 so that approximately the samenumber of lines are carrying the same message currents with a 180 phasedisplacement as without this phase displacement. In addition, theselines carrying the same currents may be uniformly distributed throughoutcable 16 so that any of the disturbed or adjacent lines 15 will beapproximately as close to a line connected to bus bars 3 as to a lineconnected to bus bars 4. In this manner the resultant crosstalk includedin any of these adjacent lines will be substantially neutralized.

It is to be understood that :the cross-sectioned portion of the cable 16represented by 17 in the drawing is composed of other lines similar to11, 12, 13, 14 and 15. These lines may be either connected to otherequipment such as 18, or evenly distributed between bus bars 3 and 4.However, they have not been individually shown, but rather shown incross-section so that the distribution of the typical lines illustratedmay be easily and clearly shown.

Fig. 2 shows an arrangement of the second type, in which greatertemporary phase displacements are obtained by using, for example, acommon steel wire of a telegraphone carrying the broadcast transmissioncurrents to magnetic recording device 5. Telegraphone pick-up devices,for example, 6-9, spacially separated from each other lead to diiferentlines or bus bars. In case there are only a small number of linessimultaneously transmitting the same message currents it would probablybe desirable to provide a pick-up device for each individual line.However, in the case of a very large number of lines simultaneouslytransmitting the same message currents, it would be desirable to dividethese lines into groups, each group being connected to bus bars whichare supplied from an individual pick-up device. Thus, the signals whichcomprise the entire message as transmitted over each of the differentlines or groups of lines are displaced by small time intervals so thatthe peaks of the signal currents in the different groups do not occursimultaneously. Then the total cross-talk induced in disturbed circuitsis not the numerical sum of the instantaneous cross-talk currentsinduced by each of the disturbing circuits. In this manner multipletransmission may be efiected with a normal level of current'in each ofthe disturbing circuits or lines without increasing the cross-talkinduced in the disturbed circuits or lines above the level encounteredwhen the disturbing circuits are all carrying diiierent signalssimultaneously. A special recording device 10 would be provided toremove the magnetism of the steel wire produced by the signals when thewire passes recording device 5.

Instead of using the steel wire greater time retardations may beobtained by apparatus such, for example, as that shown in Fig. 3 inwhich electrical delay networks K are provided. In order a that auniform delay of the total voice frequency band may take place, thedelay networks may be formed by the series connection of an artificialcable with a phase balancing circuit. Details of representative delaynetworks and circuit arrangements suitable for use in these circuits maybe found in the disclosures of the following U. S. patents; H. Nyquist,1,607,687, November 23, 1926, H. Nyquist, 1,770,422, July 15, 1930, H.W. Bode, 1,828.454, October 20, 1931.

As illustrated in Fig. 3, the source of the sig .nals to be distributedis connected to bus bars I to which a group of lines illustrated bylines 19 and 20' are connected as well as a group of current delaydevices two of which are illustrated by delay network K which arerepresented in Fig. 3' at 25 and 26. These networks 25 and 26 delay theentire frequency band which is transmitted by different amounts. Theoutputs of these delay networksare connected through amplifiers V tocompensate for the attenuation of these networks and are showndiagrammatically at 27 and 28 in Fig. 3. The outputs of these amplifiersare connected to other bus bars II and III respectively. Connected toeach of these bus bars is a group of lines, two of which are shown forpurposes of il lustration in Fig. 3 which are 21 and 22, and 23 and 24,respectively. As described above, these lines may also be distributedthroughout the cable. This is illustrated in the figure in which only afew of the lines of cable 16 are individually shown in order that thedistribution may be clearly illustrated. Furthermore, it is an advantageto evenly distribute the line carrying the same current evenly betweenthe bus bars as shown in Fig. 3 in which two lines are connected to eachof the bus bars.

The invention is of particular importance for broadcasting systems. Inorder that the lines which are not employed for broadcasting but fortelephony may have the smallest possible crosstalk, it is necessary tohave as uniform as possible a distribution of the texts transmitted withdifferent phase over the subscribers lines.

What is claimed is:

1. Means for reducing the cross-talk in multiple lines several lines ofwhich carry the same message, comprising a telegraphone, several pickupheads associated therewith and so related that they each receive theentire message with a slightly different time displacement, each of saidpickup heads being connected to one or more lines of the several lines.

2. A method of reducing cross-talk in a multiple transmission systemwherein the same message is simultaneously transmitted over a group ofadjacent transmission lines, which comprises, transmitting the entiremessage over each individual line of the group of lines with a differentphase displacement.

3. A method in accordance with claim 2, characterized in this that boththe fundamental and over tones of the entire message as transmitted bythe individual lines are displaced by the same phase angle.

4. A method according to claim 2 in which the entire message istransmitted over each line of the group of lines with a different timedisplacement.

5. A method in accordance with claim 2, particularly for broadcasting,characterized in this, that the phase displaced messages are uniformlydistributed to the individual lines of the group 7 of lines transmittingthe same message.

6. The method of reducing cross-talk disturbances in a multipletransmission system in which the same message is simultaneouslytransmitted over a plurality of groups of adjacent transmission lines,characterized in this that the entire message is transmitted over eachgroup of lines with a different phase displacement;

'7. The method of reducing cross-talk disturbances in a multiplebroadcasting system in which the same message is simultaneouslytransmitted over a plurality of adjacent groups of transmission lines ina cable, comprising transmitting the entire message over each group oflines with a different time displacement and uniformly distributing thegroup of lines transmitting these time displaced messages through thecable.

8. In an electrical communication system comprising a source of messagecurrents, a plurality of adjacent transmission lines, a group of currentdelay devices connected to said source of message currents and to agroup of said transmission lines, the method of reducing the cross-talkinduced from said group of lines into the other adjacent lines whichcomprises transmitting all the message currents over each transmissionline of said group of lines with a different delay.

9. In an electrical communication system comprising a source of messagecurrents, an electrical communication cable comprising a plurality ofadjacent transmission lines, a group of current delay devices eachconnected between a group of said transmission lines and said source ofmessage currents, a method of reducing the cross-talk between saidgroups of lines and the remainder of the lines of said cable whichcomprises transmitting all the message currents over each line of saidgroup of lines and delaying the message currents transmitted to saidlines a different amount.

10. In an electrical communication system comprising a source of messagecurrents, an electrical communication cable comprising a plurality ofadjacent transmission lines, a group of current delay devices eachconnected between a group of said transmission lines and said source ofmessage currents, a method of reducing the cross-talk between saidgroups of lines and the remainder of the lines of said cable whichcomprises transmitting the message currents over each group of lineswith a different delay and uniformly distributing the lines of saidgroups of lines throughout said cable.

11. In a communication system, comprising a. plurality of adjacenttransmission lines, several lines of which carry the same messagecurrents, means for reducing the cross-talk between the several linescarrying the same message current and the remainder of the lines of saidtransmission lines which comprises electrical delay networks andrepeaters so designed and so connected to the several lines that theentire message will be transmitted over each of the several lines with aslightly difierent time displacement.

MAX LANGER. WILHELM RABANUS.

